Electron discharge device



N 13, 1934- s. w. DODGE, JR

ELECTRON DISCHARGE DEVICE Filed Sept. 7, 1933 HHHHII FIG. I

INVENTOR s.w. DODGE, Jr

B w/ 'w ATTORNEY Patented Nov. 13, 1934 UNITED STATES PATENT OFFICE Applcatlon September I, 1933, Serial No. 688,428

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My invention relates to electron discharge devices and more particularly to thermionic cathodes for such devices.

The principal object of my invention is to pro-= 5 vide a. high power output electron discharge device having a thermionic cathode of very great elfectivc surface and comprising a plurality oi filament strands mounted side by side and connected either in parallel or series parallel, the cathode being held by a simple and rugged construction which maintains the cathode strands in proper relation to and alignment with one another and with the other elements of the device at all times. Other objects and advantages will appear from the following description.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which,

Figure 1 shows a partial longitudinal section of an electron discharge device embodying my in-- vention, with parts of the grid and plate broken away to show the cathode; Figure 2 is a perspective view of some details of the cathode support; Figure 3 is a perspective view of a partly formed mum-filament cathode made in accordance with my invention; Figure 4 is a. perspective view of 39 an apparatus made in accordance with my invention for forming the cathode; and Figure 5 is a perspective view or a finished cathode.

Referring to the drawing, the electron discharge device shown in Figure 1 has a dome type evacu- 35 ated envelope or bulb with a re-entrant stem 11 and the usual base 12. A pair of plate side rods 13 support a flat type plate 14 having the usual longitudinal ears or plate side rod channels on its opposite edges. A top mica spacer 15 with a slot 16 and a bottom mica spacer 17 with a slot 18 are mounted at opposite ends of the plate to extend transversely of the bulb and to be parallel to each other, with said slots in alignment and extending lengthwise of the flattened plate 14. The mica spacers are supported from the plate, preferably from the plate side channels by metal loops or straps 19 which embrace the spacers and are welded to the plate channels 15. The grid 20, of the usual fiat type, is concentric with the plate and has its side rods 21 mounted on the stem 11.

The cathode, which is coaxial with-and surrounded by the grid 20, comprises a plurality of strands or filament wires 22 arranged side by side and constituting two groups, the strands in each group being connected in parallel, and the two groups being connected in series. The filament wires 22, which project through the slots 16 and 16 in the mica spacers, are stretched between two metal bottom rods 23 and 24, mounted end to end on the stem 11 below the bottom spacer 17 and in client with the bottom slot 18, and a top rod 25 mounted above the top spacer 15 parallel to the bottom rods 23 and 24 and in alignment with the slot 16 in the top spacer. The cathode strands 55 22 extend side by side from both bottom rods to the top rod, the strands extending from one bottom rod 23 constituting one group, and the strands from the bottom rod 24 constituting the other group, the two groups being connected in series through the top rod 25 which is common to both groups. I prefer to make the wire constituting the strands of the cathode into a series of elongated loops with their bights engaged by the top and bottom rods. These loops mounted side by side and connected in parallel, have considerable surface for emitting electrons, and the cathode made with these loops side by side is in effect a thin flat cathode substantially coextensive with the grid 21.

In order to keep the cathode strands between the top and bottom rods taut, the top rod is resiliently supported so as to be yieldingly pulled away from the bottom rods. One desirable. con struction for the purpose is that shown in the drawing, in which the ends of the top rod 25 are slidable up and down in slotted guides 26 mounted on the top mica spacer 15 at opposite ends of the slot 16 to be perpendicular to the spacer. The guides 26 permit the top rod to slide bodily up and down in the plane of the cathode strands. A con venient form of slotted guide is the inverted U-shaped guide shown in the drawing. The tension device or means for keeping the cathode strands under tension comprises a bridge or channel member 27 mounted on the upper side of the top mica 16 in registry with the slot 16 preferably by being supported at its ends on the U-shaped guides 26, and coil springs 28 positioned on the bridge or channel member 2'7 to we engage the top rod 25. The coil springs pull up on the top rod 25, and thus maintain the cathode strands 22 under tension. This tension device prevents sagging of the strands 22 and short circuits between the cathode and the grid. The 105 guides 26 permit the top rod 25 to move bodily and parallel to itself in the plane of the cathode, but prevent it moving laterally out of the plane of the cathode, and thus maintain proper alignment of the cathode strands with the other elements in the tube. This spring and channel construction' is a very simple and rugged tensioning arrangement for maintaining the cathode strands taut at all times during operation.

A cathode embodying my invention may be made in various ways, but I prefer the simple and effective method of winding the cathode in the form of a round helix with two side rods, as shown in Figure 3, on a regular grid winding machine, and then stretching this round helix into a flattened helix on a stretching device such as that shown in Figure 4. This particular stretching apparatus comprises a pair of slides 29 movable away from each other and provided with uprights 30 with grooves at the edges for holding the side rods of the round helix shown in Figure 3. A sliding cam 31 forces the slides 29 apart into the position shown in dotted lines in Figure 4, thereby flattening the round helix into the shape shown in Figure 5. This flattened helix is then coated, for example by spraying, with an electron emitting material such as barium and strontium oxides, to make it a good electron emitter. One side rod is then out near the middle into the two bottom rods 23 and 24, as shown in Figure 5. The result is a flattened helix wound at one edge over the top rod 25 and at the other edge over the two bottom rods 23 and 24, the helical winding extending along one bottom rod 23, over the gap between the adjacent ends of the bottom rods, and along the other bottom rod 24. Each turn of the helix engages and is electrically connected to a metal rod. The electron emitting portion of the cathode thus consists of a flattened helix divided in two sections, each section having its loops or turns connected in parallel, and the two sections being connected in series through the top rod 25, as is shown in Figure l.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What is claimed as new is,-- I

1. An electron discharge device including an evacuated envelope, a pair of guides mounted at one end of said envelope and parallel to its longitudinal axis, a movable metal rod mounted with its ends in said guides to extend transversely of said envelope and to move sidewise and bodily along said axis of said envelope, two metal rods fixed near the other end of said envelope, spaced filament wires extending side by side from said movable rod to said fixed rods, a support mounted on said guides, and resilient members on said support and attached to said rod to maintain said filament wires under tension.

2. An electron discharge device including an evacuated envelope, an insulating support mounted at oneend of said envelope and perpendicular to the longitudinal axis oi. said envelope, a

.rods at the other end of said envelope, parallel filament wires connected between said rod and said fixed bottom rods, 9. member mounted on and parallel to said insulating support, and springs on said member attached to said rod for maintaining said filament wires under tension.

3. An electron discharge device including an evacuated envelope inclosing a mica spacer having a central slot and mounted to extend transversely of said envelope, a slotted guide perpendicular to said spacer at each end of said slot, a cathode comprising a movable metal rod mounted on one side of said spacer opposite the slot in said spacer with its ends slidably mounted in said guides, two fixed rods mounted end to end on the other side of said spacer, cathode wires extending side by side through said slot and between said movable rod and said fixed rods, and a tension device comprising a bridge member supported at its ends to extend lengthwise of said slot in said spacer and springs mounted on said bridge member to engage said rod and tense said cathode wires.

4. An electron discharge device comprising a sealed envelope enclosing a tubular anode positioned with its longitudinal axis lengthwise of said envelope, a mica spacer mounted near one end of said envelope on said anode to be perpendicular to the longitudinal axis of saidanode and having a slot, a pair of inverted U-shaped guides on said mica spacer at opposite ends of said slot, a cathode comprising a metal top rod mounted opposite said slot with its ends slidable in said guides, a pair of rods mounted end to end near the other end of said envelope and a plurality of cathode wires suspended side by side withinsaid anode between said top rod and said bottom rods and passing through said slot, and a tension device comprising a channel member supported at its ends by said U-shaped guides and helical springs supported by and extending through said channel member and attached to said top rod for maintaining said cathode wires under tension.

5. An electron discharge device comprising a sealed envelope having a stem, a cathode carried by said stem and comprising two metal bottom rods mounted on said stem in alignment with a gap between their ends, a metal top rod mounted parallel to said bottom rods, a filamentary conductor wound over said top rod and over both said 'bottom rods into a flattened helix which extends across said gap and has its turns in engagement with said top rod and both said bottom rods,'a current supply lead for each of said bottom rods, a resilient support on said stem for holding said top rod, and a tubular plate mounted on said stem to surround said cathode.

STEPHEN WEBSTER DODGE, JR.

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